Catalytic reforming is a process with C6-C12 naphtha fractions as feedstocks for producing high-octane gasoline blending component or aromatics and by-product hydrogen by subjecting the feedstock hydrocarbon molecules to reforming reactions such as dehydrogenation of cycloalkane, dehydroisomerization of straight chain alkane and dehydrocyclization of paraffins, etc. in the presence of hydrogen and catalysts at a certain temperature and a pressure. A supported bifunctional reforming catalyst widely adopted in current catalytic reforming technology comprises the hydrogenation/dehydrogenation function provided by a metal component and the acidic isomerization function provided by a support. The reforming catalyst is typically a bi (or multi) metallic catalyst using active alumina as the support and Pt as the major metal component, and comprising a second metal component such as rhenium, tin or germanium.
As for the bifunctional reforming catalyst, the metallic function and the acidic function act synergistically on the catalytic reforming reaction. If the hydrogenation/dehydrogenation active function of the metal in the two is too strong, carbon deposit on surfaces of the reforming catalyst will increase rapidly, which goes against the proceeding of the reforming reaction; and if the function of the metal is too weak, the activity of hydrogenation/dehydrogenation reaction will decrease. If the acidity is too strong, the hydrocracking activity of the catalyst is comparatively strong, and the liquid yield of the reforming product will decrease; and if the acidity is too weak, the activity will decrease. Therefore, the balanced match between the acidic function and metallic function of the support determines the activity, selectivity and stability of the catalyst.
In addition, as for a platinum-rhenium reforming catalyst used for semi-regenerated catalytic reforming, since the metal rhenium has a quite high hydrogenolysis activity, if the activity of rhenium is not passivated at the beginning of operation, a drastic hydrogenolysis reaction will occur in the initial state of feed supply, which releases a great amount of reaction heat to make the temperature of the catalyst bed rise rapidly and cause an overtemperature phenomenon. Once such a phenomenon occurs, serious consequences tend to be caused. Minor consequences include a large amount of carbon deposit of the catalyst, which decreases the activity and stability of the catalyst; and serious consequences include burning out the catalyst, reactor and internal components. Hence, the platinum-rhenium reforming catalyst needs to be presulfurized before feedstock injection. The excessive hydrogenolysis reaction of a fresh catalyst is reduced through presulfurization so as to protect the activity and stability of the catalyst and improve the selectivity of the catalyst. Methods for presulfurization of the platinum-rhenium catalyst include two types, one of which introduces H2S into hydrogen and carries out presulfurization of the catalyst slowly under certain temperature and pressure, and the other of which injects organic sulfides such as dimethyl disulfide and dimethyl sulfide and so on into hydrogen under certain temperature and pressure and uses H2S formed after decomposition of these organic sulfides for presulfurization of the catalyst. The first method is usually used in laboratory investigation. The second method is widely used for a start-up of industrial devices of the platinum-rhenium catalyst. These two methods both have the nature of presulfurizing the catalyst with H2S and both pertain to gas-phase sulfurization. The presulfurization of the platinum-rhenium reforming catalyst has problems of equipment corrosion, environmental pollution and security risks and the like.
The existing technologies for regenerating reforming catalyst, as disclosed in USP20120270724, include catalyst coke-burning, oxychlorination and reduction.
The sulfur content in the feed needs to be strictly limited during the process of using the reforming catalyst and is usually required to be less than 1 ppm. If sulfur poisoning occurs during the process of using the catalyst, and the sulfur absorbed on the catalyst is oxided to form sulfate ion, it is generally considered that the performance of the catalyst will be hurt. Therefore, sulfur on the catalyst needs to be removed before the catalyst coke-burning. It is usually removed by means of the recycle hydrogen used at a higher temperature after the feed to the reformer is stopped, so as to avoid the production of sulfate ion during the coke-burning process. Or after sulfate ions in a certain content are produced, the sulfate ions need to be removed.
CN98117895.2 discloses a method of removing sulfate ions from the reforming catalyst, comprising introducing at 400° C. to 600° C. organic chlorine compounds, which are decomposed into hydrogen chloride under said condition, into the catalyst poisoned with sulfate ions so as to remove them. This method can effectively remove the sulfate ions in the catalyst compared with the conventional regeneration of the catalyst by oxychlorination.